The invention relates to the cross-sectional configuration of a transverse girder on a roof luggage carrier of a vehicle.
Roof luggage carriers are generally made of transverse girders placed crosswise over the roof which are held and supported on support legs on the sides of the roof. In conventional vehicles the support legs are attached by means of tensioning clamps to the rain gutters of the roof. In modern, aerodynamically optimized vehicles, no roof gutters are provided so that other and more expensive designs with support plates and tensioning clamps are required (DE-OS 34 06 431). Furthermore vehicles, in particular utility vehicles and off-the-road vehicles with a roof railing consisting of railing pipes extending o either side of the roof are known. In that case too, roof luggage racks consist of transverse girders which are connected to the railing pipes through tensioning devices.
In all of the above-mentioned designs of roof luggage carriers transverse girder are used as bearing rails extending above and at a distance from the vehicle roof at a right angle to the direction of travel.
Conventional transverse girder have cross-sections with square or rectangular profiles (DE-PS 35 16 483; DE-PS 31 04 163) or with round profiles (DE-PS 35 10 805). Obviously the aerodynamic characteristics of a vehicle are generally affected by such transverse girder extending at a right angle to the direction of travel above the vehicle roof. Also travel noise is generally increased due to the unfavorable flow of the oncoming air around the transverse girder.
Particularly unfavorable conditions exist with the usual, square or rectangular cross-sectional configurations of the transverse girder, where strong eddy currents at the edges cause an especially high noise level during rapid travel. The performance of the known round cross-sections is not much better.
In order to improve this situation, a known device (DE-OS 36 07 856) provides a cross-section for the transverse girder that is egg-shaped or drop-shaped. A better aerodynamic form with a reduction of the noise level is achieved. Further measures to improve the aerodynamic characteristics consist in providing forms that merge into each other in a flat surface between transverse girder and supporting legs, and by providing covering caps on the supporting legs.
With the above-described egg-shaped or drop-shaped cross-section the symmetrical axis is horizontal above the roof of the vehicle, with the arc of least curvature pointing in the direction of travel. The arc with the greatest curvature, i.e. with the shortest curvature radius, is pointed to the back of the vehicle. Due to an essentially symmetrical form with respect to a horizontal plane, approximately the same amount of arriving air is, in principle, deflected above and below the transverse girder profile. Especially the air flow deflected down towards the roof causes relatively loud wind noises to be produced even with this profile configuration. In order to obtain a stable profile with a suitably high bearing capacity, an extruded profile with a vertical standing continuous inner wall is provided.
Accordingly, an object of the present invention consists in achieving further improvement of the vehicle's aerodynamic characteristics and reducing the noise level on an installed roof luggage carrier by means of a suitable cross-sectional configuration of the transverse girder.